The hottest mechanical alloying and its applicatio

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Mechanical alloying and its application in ultra-fine hard materials

mechanicalalloying (MA) is a powder making technology for preparing alloy powder or composite powder with equilibrium or non-equilibrium phase composition from elemental powder. It is in the high-energy ball mill, through the long-term intense grinding between powder particles and between powder particles and grinding balls, the powder is broken and torn, and the formed new surfaces are gradually alloyed by cold welding with each other. The process is repeated, and finally the purpose of mechanical alloying is achieved

mechanical alloying was developed by Benjamin et al. Of American international nickel company in the late 1960s. At that time, it was mainly used to prepare nickel based and iron-based superalloys with precipitation hardening and oxide dispersion hardening effects at the same time. In the early 1980s, American scientist Koch and his colleagues successfully obtained ni60nb40 amorphous powder by mechanical alloying. Since then, this method has developed rapidly. After a lot of experimental research, hlum and ewe proposed mechanical alloying method to prepare nanocrystals in 1988. Later, fecht and others successfully prepared nano ultrafine grained alloys by mechanical alloying, creating a new field of mechanical alloying technology. Now, the mechanical alloying method has been successfully applied to the preparation of nano ultrafine grained dispersion strengthening materials, magnetic materials, superconducting materials, amorphous materials, nanocrystalline materials, light metal high specific strength materials and supersaturated dispersed solid solutions. The United States, Germany, Japan and other developed countries have invested a lot of human, material and financial resources, done a lot of research work, achieved remarkable results, and have achieved industrial production. Inco of the United States has built a mechanical alloying production line of iron, nickel and aluminum based oxide dispersion strengthened alloys, with a production capacity of 350t/year. The research on mechanical alloying in China has made remarkable progress since 1988

mechanical alloying

1 basic principle

in 1988, Hideo Shinya of Japan proposed a calendering and repeated folding model. When the one-time reduction rate is 1/a, after n times of calendering, its thickness changes from the original d0 to D, and d=d0 (1/a). If the powder of the two elements is mixed and calendered for 10 times by mechanical alloy method and set at 1/a 316296, the particle size of the powder can be reduced to one hundredth of its original thickness, forming a very small double-layer overlap. After more calendering, the powder can reach the nanoscale microstructure. Therefore, the mechanical alloying method may also cause the powder to be alloyed in the solid state. In 1990, Atzmon proposed another principle of mechanical alloying? The mechanism of mechanical induced self propagating reaction is that intermetallics are not a process of nucleation and growth, but formed by sudden explosion. Because the ignition temperature of combustion self propagating reaction is related to the powder particle and grain size, the ignition temperature decreases with the decrease of powder particle or grain size. When the powder particles or grains are reduced to a certain extent, the local high temperature generated by mechanical collision during ball milling can ignite the powder, which is manifested as the sudden explosion of the alloy

now, it is generally believed that most mechanical alloying processes in ball milling are controlled by diffusion. The basic process of mechanical alloying is the repeated mixing, crushing and cold welding of powder particles. The mixture of several metallic or non-metallic element powders will form high-density dislocations in the process of ball milling, and the grains will be gradually refined to nano scale, which provides a fast channel for the mutual diffusion of atoms. Under certain conditions, the nucleus of the alloy phase can be formed. In the further ball milling process, until all element powders form alloy phase, and gradually grow up

2 mechanical alloying equipment

mechanical alloying equipment mainly includes vibrating ball mill, planetary ball mill and stirring ball mill

3 characteristics of mechanical alloying

(1) sudden temperature rise due to the high heat of formation of different element powders during mechanical alloying, there will be a sudden temperature rise during ball milling

(2) local melting during mechanical alloying, due to exothermic chemical reaction and high temperature, local melting of powder will occur

(3) amorphous mechanical alloying may occur under appropriate conditions. Mechanical alloying reduces the amorphous formation energy, promotes the transformation of disordered phase to amorphous, and produces a large number of defects due to repeated mechanical deformation during ball milling, thus inducing the formation of amorphous

preparation of ultrafine hard materials by mechanical alloying technology

1 ultrafine hard materials nanocrystalline cemented carbide

because of its small grain size and great grain boundary density, it shows a series of excellent properties. For example, it has not only high hardness and wear resistance, but also high strength and toughness. It has been widely used in the manufacturing of micro drills, precision tools and molds and difficult cutting fields. One of the key technologies for producing nanocrystalline cemented carbide is to prepare nano WC powder or WC Co composite powder. At present, the main methods of preparing nano cemented carbide powder are: spray conversion method, plasma method, low temperature reduction carbonization method, sol-gel method and double salt precipitation method, but the process of these methods is more complex. Since yermakov found that mechanical alloying can be used as a process to prepare amorphous alloys in the early 1980s, there has been a worldwide upsurge of research on mechanical alloying. In 1989, Ru rgers University in the United States took the lead in developing nanostructured cemented carbide and its process. By 2020, the total output value will reach 2billion yuan, and applied for a patent in the same year. Since then, large companies in Sweden, Germany, Japan and other countries have introduced their own nanostructured ultra-fine cemented carbides. Mechanical alloying can be used to prepare intermetallic compounds, amorphous, Quasicrystal Materials and nano materials, and the process is simple, which can realize industrialization. Therefore, it is a new process that has attracted much attention recently

mechanical alloying is to realize alloying in the solid state, without the restriction of gas phase, liquid phase, vapor pressure, melting point and other physical characteristics of substances, which makes it possible to realize the alloying of some substances that are difficult to be achieved by traditional smelting process in the past, and the quasi steady state, non-equilibrium state and synthesis of new substances that are far from thermodynamic equilibrium. Therefore, mechanical alloying has attracted great attention in theory and application. Tang Rong [14] et al. Pointed out that there are advantages in preparing ultrafine cemented carbide powder by mechanical alloying technology; The grain growth inhibitor Cr3C2 and cobalt are evenly distributed in WC, the composition is easy to control, the process is simple, and the cost is low

2 preparation and its influence on materials

the preparation of nano powders by mechanical alloying is a very effective and simple method. There are two ways to form nanocrystals by mechanical alloying: ① nanocrystals are formed by mechanical alloying of coarse-grained materials; ② Amorphous materials are mechanically alloyed to form nanocrystals

coarse grained powder is milled by high-strength mechanical milling, resulting in a large amount of plastic deformation and high-density dislocation. In the initial stage, the dislocations in the powder after plastic deformation are first tangled together, forming dislocation entanglement. With the increase of ball milling strength, the deformation of powder increases, and the entangled dislocations move to form dislocation cells. The high-density dislocations are mainly concentrated in the surrounding area of the cells, forming cell walls. At this time, the deformed powder is composed of many dislocation cells, and there is a small difference between cells. With the further increase of mechanical alloying strength, the deformation of powder increases, the number of dislocation cells increases, the size decreases, and the average orientation difference across the cell wall also gradually increases. When the deformation of the powder is large enough, the dislocation density constituting the cell wall increases to a certain extent, and the orientation difference between cells reaches a certain extent, the cell wall changes to grain boundaries to form nanocrystals

The crystal growth of amorphous powder in the process of mechanical alloying is a process of nucleation and growth. Under certain conditions, crystals are an important gateway for countries to open to ASEAN, nucleating in amorphous matrix. The growth rate of crystal is low, and its growth is limited by severe plastic deformation caused by mechanical alloying. Due to mechanical alloying, there are many nucleation positions in the amorphous matrix and the growth rate is low, so nanocrystals are formed

the effects of mechanical alloying technology on materials are mainly as follows: ① highly dispersed second phase particles can be formed; ② It can expand the solid solubility of the alloy and obtain supersaturated solid solution; ③ It can refine the grains, even reach the nanometer level, and change the morphology of the powder; ④ Alloy powder with new crystal structure, quasicrystal or amorphous structure can be prepared; ⑤ The ordered alloy can be disordered; ⑥ It can promote the chemical reaction at low temperature and improve the sintering activity of the powder

the synthesis of nano powder by mechanical alloying is simple and efficient, and the particle size of the prepared powder is small, but it often causes powder pollution due to friction with the tank and ball

application and Prospect

since the advent of cemented carbide, there has been an irreconcilable contradiction between its strength and hardness, and the rapid development of advanced manufacturing technology strongly requires the combination of the two. The research shows that when the WC grain size is reduced to submicron and should be equipped with lifting holes or lifting rings, the hardness, wear resistance, strength and toughness of cemented carbide materials are improved. This ultra-fine grained WC Co cemented carbide is vividly called double high cemented carbide because of its high hardness, high bending strength, high wear resistance and high toughness. It meets the increasingly high requirements for high-performance cemented carbide tool materials, and is becoming a hot spot of competitive research and development in the international engineering field. The preparation process of alloy powder, sintering process and material detection technology have developed rapidly

ultrafine grained cemented carbide has high hardness, high wear resistance, high strength and toughness, and can be stably produced in large scale. It is very suitable for the technical requirements of modern advanced manufacturing technology for high-performance tool materials. It has become a hot spot in the development of international engineering materials, and is widely used in the field of high-efficiency and high-precision machining in automobile manufacturing, aerospace, mold manufacturing, electronic information and other industries. For example, there is a great demand for double high-performance ultra-fine grained cemented carbide for hole machining tools for automobile processing and micro drills for printed circuit boards. With the rapid development of the electronic information industry, the demand for micro drills is increasing. The monthly demand is about 25 ~ 35 million pieces, and the annual demand for micro drill bar material is about 1800 ~ 2000t. The demand in the domestic market is increasing at the rate of 140% per year, and the demand in the international market is increasing at the rate of 5%. In terms of cutting tools for the automotive industry, taking the demand of Shanghai Automotive Industry Group as an example, at present, the annual consumption of high-performance cemented carbide cutting tools is US $30million, which is converted into about 100 ~ 150t billets, and shows a rapid upward trend

at present, international famous cemented carbide production enterprises such as Sandvik in Sweden, Kennametal in the United States, Plansee in Austria, forecreu in France and Toshiba tungaloy in Japan have entered and occupied the market of ultra-fine grained cemented carbide bars and their hole processing tools in China. Some scientific researchers in China have also carried out research and development in this field and made important progress. The grain size of cemented carbide (SRIM) developed and produced in small batch by Shanghai Institute of materials has reached 0.3 ~ 0.5 m, realizing double high performance. More than 10 bar specifications of 5 ~ 40mm have been produced, of which about 60% are with internal cooling holes. It has been made into various forms of special tools, which have been successfully applied in the automobile industry and have obtained the same model as the original import

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